Miniature adjustable attenuator

ABSTRACT

A high frequency attenuator is provided having flat characteristics from direct current to frequencies of the order of 4 GHz and having attenuation adjustable in steps. This is accomplished by securing a plurality of thick film resistive unit pads around a central rotary hub, each pad consisting of a ceramic substrate rectangular in configuration with a fired thick film shunt resistive element supported on the substrate on one face thereof, a pair of fired silver strips also on the face of the substrate contacting the shunt resistive element, a coating of fired silver material completely covering the reverse face of the substrate except for that portion directly opposite the shunt resistive element, and fired silver layers on the edges of the substrates with the inner edges grounded to the central hub. The hub is rotatably mounted in an outer cylindrical housing composed of conductive material. Exposed flexible electrical conductor means surround the resistive units, providing ground connections between the outer conductive edges of the substrates and the outer housing. There is a plurality of fixed terminals on the rotor and a plurality of coaxial transitions are connected between the ends of the silver strip layers and fixed terminals mounted on the rotor. Each fixed rotor terminal is adapted to engage a fixed blade attached to the central conductor of a coaxial connector as the rotor is rotated to select a given attenuator pad.

United States Patent [191 Keranen Apr. 16, 1974 1 MINIATURE ADJUSTABLE ATTENUATOR Robert M. Keranen, Tustin, Calif.

[73] Assignee: Telonic Industries, Inc., Laguna Beach, Calif.

22 Filed: Nov. 6, 1972 21 Appl. No.: 303,881

[75] Inventor:

Primary Examiner-Harold Broome Assistant Examiner-David A. Tone Attorney, Agent, or Firm-Fowler, Knobbe & Martens [57] ABSTRACT A high frequency attenuator is provided having flat characteristics from direct current to frequencies of the order of 4 GHz and having attenuation adjustable in steps. This is accomplished by securing a plurality of thick film resistive unit pads around a central rotary hub, each pad consisting of a ceramic substrate rectangular in configuration with a fired thick film shunt resistive element supported on the substrate on one face thereof, a pair of fired silver strips also on the face of the substrate contacting the shunt resistive element, a coating of fired silver material completely covering the reverse face of the substrate except for that portion directly opposite the shunt resistive element, and fired silver layers on the edges of the substrates with the inner edges grounded to the central hub. The hub is rotatably mounted in an outer cylindrical housing composed of conductive material. Exposed flexible electrical conductor means surround the resistive units, providing ground connections between the outer conductive edges of the substrates and the outer housing. There is a plurality of fixed terminals on the rotor and a plurality of coaxial transitions are connected between the ends of the silver strip layers and fixed terminals mounted on the rotor. Each fixed rotor terminal is adapted to engage a fixed blade attached to the central conductor of a coaxial connector as the rotor is rotated to select a given attenuator pad.

13 Claims, 12 Drawing Figures PATENFEU APR 1 6 I974 SHEET 1 BF 4 PATENTEDAFR 16 I974 3 805 20 9 SHEET u I]? a MINIATURE ADJUSTABLE ATTENUATOR PRELIMINARY DESCRIPTION In carrying out the invention in accordance with a preferred form thereof, a plurality of attenuator pads formed on flat plate substrates are mounted on the periphery of a rotor hub mounted rotatably within a cylindrical housing, which is provided with openings to receive input and output coaxial connectors. Suitable means are provided for connecting any selected one of the attenuator pads to the coaxial connectors by rotating the rotor hub. In this manner a variable attenuator is provided adjustable in steps according to the angular position of the rotor hub, by so forming each attenuator pad that it has a different attenuation from the adjacent one. 7

Turret-type, step-wise adjustable, coaxial-line attenuators have been proposed in the past, and attenuators have been proposed in which coaxial line type attenuators of different degress of attenuation are provided with switching connections for selecting one or more of the coaxial line attenuators. However, I have found that a higher degree of stability, lower VSWR and more compact construction, requiring less bulk and volume, can be accomplished in accordance with my invention. One of the significant features of the illustrated embodiment of the invention is the employment of flat attenuator pads and the mounting of the attenuator pads in the space between a rotor hub and the inner surface of a cylindrical housing so that grounding connections may be made between each edge of the pad and the adjacent rotor hub or inner surface of the enclosing housmg.

To this end the pads are formed with suitable shunt and series resistance elements in the form of thick films deposited upon one surface of a substrate. There is a ground-plane silver coating on the reverse surface of the substrate with the silver coating continuing around the edges of the substrate so that the ground plane is provided with a ground connection to the rotor hub and the outer housing through the silver coated edges of the substrate. Moreover, the silver edge coating laps over the front surface of the substrate very slightly at the central portion thereof for forming the ground connections for the shunt resistive element of the attenuator pad. Series resistance for the pad is formed by thick-film, silver microstrips extending lengthwise in the center portions of the front surface of the substrate. Transition elements are deposited at the appropriate portions of the substrate for providing compatible electrical connections and mechanical union between the silver strips and the center of the shunt resistive element as well as between the silver strips and through pins which are employed for making connections to the center conductor in a coaxial transition to coaxial connectors mounted upon the outside of the enclosing housing.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the accompanying drawing:

DRAWING In the drawings: FIG. I is a perspective view of an embodiment of the invention;

FIG. 2 is an exploded perspective view of the components of the structure of FIG. 1;

FIG. 3 is a view of a section through the structure of FIG. 1 represented as cut by a longitudinal plane through the central axis of the cylindrical housing illustrated in FIG. 1;

FIG. 4 is a view of a cross-section of the structure represented as cut by a transverse plane 44 indicated in FIG. 3;

FIG. 5 is a view of a cross section of the rotor hub illustrated in FIG. 3 represented as cut by a plane 5-5 indicated in FIG. 3 and also illustrating fragmentarily a switch blade for making connections with contacts mounted upon the rotor;

FIG. 6 is a fragmentary view of a portion of the rotor represented as cut by a plane 66 indicated in FIG. 3

and showing primarily the construction of the coaxial transition between the microstrip series attenuator element of a pad and a switching contact button, and illustrating a through pin forming the center conductor of a coaxial transition element;

FIGS. 7-11, inclusive, represent various steps in the formation of an attenuator pad in accordance with the invention;

FIG. 7 is a perspective view of a rectangular substrate upon which the appropriate resistance and ground plane elements are deposited to form a pad;

FIG. 8 is a plan view of the substrate of FIG. 7 shown inthe form after thick film microstrips have been applied thereto;

FIG. 9 is a view of the substrate after two additional steps have been taken in the formation, namely the step of depositing the ground plane on the reverse surface of the substrate (not visible in FIG. 9) and the next step of depositing transition elements for the ends of the silver microstrips;

FIG. 10 illustrates the next step in the formation of a pad after the shunt portion or resistive element has been deposited, extending transversely across the center portion of the microstrip between the edges thereof and the center transitions for the silver microstrips;

FIG. 11 is a view of the reverse face of the substrate of FIGS. 7 and 8 after the ground plane has been deposited thereon and before the transitions of FIG. 9 have been deposited; and

FIG. 12 is a view of another embodiment of the pads formed in accordance with the invention, differing from FIG. 10 in that a plurality of shunt elements or transversely extending resistive elements are provided in order to provide a considerably higher degree of attenuation than the embodiment of FIG. 10. Each form of pad is employed as one of selectively different pads of assembled structures of FIGS. 1, 2, 3 and 4.

Like reference characters are utilized throughout the drawing to designate like parts.

DETAILED DESCRIPTION As illustrated in FIGS. 1-4, a microwave attenuator in compact form, adjustable in steps, is wholly enclosed in a small housing I] having a cylindrical inner surface. Concentrically mounted therein is a rotor 12 comprising a shaft 14 and hub structure 13, shown as integral, having secured thereto a plurality of attenuator pads 15-23 inclusive and a section of coaxial transmission line 24, without attenuation. The rotor structure 13 includes a shaft portion 25 carrying a control knob 26 and includes suitable mechanism including a ball detent 27 cooperating with an indexing plate 28 to index the rotor in various positions according to which attenuator pad is to be connected in the circuit.

The housing 1 1 has an outer surface, which is also cylindrical except for a portion 31 which is flattened to enable coaxial connectors 32 and 33 to be mounted thereon opposite lateral openings 34 and 35 formed in the housing 11. As will be explained, suitable contacts are provided for enabling the coaxial transmission line connectors 32 and 33 to be connected to any selected attenuator pad according to the indexed position of the rotor structure 13.

Except for the degree of attenuation and the number of shunt resistive elements, all of the attenuator pads are similar in construction and in principle of operation. The invention, therefore, will be described by description of the minimum attenuation pad 15, a plan view of which appears in FIG. 10.

The attenuator pad 15 illustrated in FIG. comprises a substrate 37 upon which silver microstrip conductors 38 have been deposited to form conductive elements, transitions 39 have been deposited for the outer ends of the microstrips 38, and transitions 40 have been deposited for the inner ends'of the microstrips 38, as well as for a resistive element 41. A silver ground plane coating 42 has also been deposited upon the substrate 37 and the ground plane layer 42 also continues along the edges of the substrate 37 toform edge-strips 43 of silver. In addition there are overlapping terminations or tab portions 44 which electrically contact the edge strips 43 and which partially overlap the center portion of the front face of the substrate 37 for electrically contacting the ends of the shunt element 41. However, in depositing the ground plane coating 42 a blank space 45 is left upon which there is no electrically conducting deposit in order to avoid capacitative effects with respect to the resistive element 41.

The dielectric and conductive elements of the attenuator pad may be composed of suitable material to provide the desired properties. Where it is desired to provide a relatively low cost, compact, step-wise adjustable attenuator having an external housing diameter of approximately 1.3 inch and a housing length of approximately 2.15 inches the microstrip conductors may consist of thick film silver having composition of approximately 62 percent silver in a suitable binder. Satisfactory results have been accomplished where the substrate comprises approximately 96 percent alumina, the microstrips 38 and the ground plane material 42 comprise silver of a resistivity of less than 0.003 ohms per square of a type sold by E.I. Dupont DuNemours Co. under the designation, Dupont No. 6320, the terminations 39, 40 and 44 comprise a a palladium-gold composition sold by the Dupont DuNemours Co. under the designation Dupont No. 8651, and the resistive element 41 is dimensioned to provide 100 ohms per square composed of a material sold under the designation Dupont BIROX No. 1221.

The foregoing illustrative formulation is for an attenuator element having a characteristic impedance of 50 ohms where the series resistance of the resistive mate-.

rial is 5.75 ohms and the shunt resistance to the ground plane from either transition node 40 is 436.0 ohms. It will be understood that the other attenuator pads of the group 16-23 inclusive will have successively greater series resistance and successively smaller shunt resistance, varying for example, from 1 1.46 series ohms to 81.82 series ohms and 221.0 shunt ohms to 51.0 ohms for producing attenuations of successively 1,2,3,4,5,6,7,8,9,10, 15 and 20 decibels, e.g., with appropriate changes in dimensions of the resistive and conductive elements which will be described in further detail hereinafter.

The preferred method of forming the attenuator pad is as follows: The conductive or resistive material is utilized in finely divided or powdered form bonded with a glass frit, screened and then fired at high temperature.

The first step in the assembly process is screening the microstrips 38 on to the dielectric substrate 37 as illustrated in FIG. 8. Then the transitions or terminations 39, 40 and 44 are screened onto the substrate so as to cover the ends of the silver microstrip conductors 38, making mechanical and electrical contact therewith. Before or after these steps are accomplished, the ground plane covering 42 and the edge silver covering 43, are also screened upon the surfaces of the dielectric substrate 37 as indicated in FIGS. 11 and 9.

Thereafter the resistive element 41 is screened upon the substrate 37 so as to make electrical and mechanical contact at the center with the transition 40 and at the end with the transitions 44. The material of which the transitions 39, 40 and 44 is composed is specially selected to become compatible with respect to both electrical contact and mechanical adhesion with the silver microstrip 38 and the resistive element 41.

Preferably the deposition by screening of elements 38, 39, 40, 41 and 44 is accomplished by a very accurate screening machine with stainless steel screens containing the desired pattern. A paste containing the desired composition of metal particles and glass frit is pressed through the screen and the paste burns off upon firing at approximately 850 C. This results in coatings about one mil thick before firing and about 0.6-0.7 mils thick after firing.

As previously indicated an attenuator with a greater degree of attenuation may be produced by changing the dimensions of the microstrips 38 and the resistive element 41. However, for pads greater than 20 dB the required dimensions of the resistive element increases in a non-linear fashion and it has been discovered that attenuations up to at least 100 dB can be achieved with a pad of minimal dimension by utilizing plural resistive elements of 20 dB or less. For example, for attenuations of 30 and 40 dB. there may be two resistive elements and for greater attenuations there may be three resistive elements or more. For example, there may be four resistive elements for and dB. and five resistive elements for and dB. attenuation.

An example of a multiple arrangement for providing, for example, 70 or 80 decibels is illustrated in FIG. 12 wherein there are three resistive elements 46, laid upon and partially overlapping transitions 47 to make electrical contact with them and corresponding in purpose and composition to the transitions 40 of FIG. 10. The transitions 47 in turn have been laid upon and partially overlap sections 48 of silver microstrip material corresponding to the microstrips 38 of FIG. 10. In the case of the multiple arrangement of FIG. 12, more than one of the overlapping ground plane tabs such as the tab 44 of FIGS. 9 and 10 may be provided for contacting the shunt resistive elements 46. If desired, as shown, the edge strip material 43 may overlap the front face of the dialectric substrate 37 along continuous narrow strips 7 49.

The attenuator pads to 24 inclusive are secured to the rotor 13 with the inner silver edges 43 electrically joined to the rotor to ground the plane 42. For example, conductive epoxy cement 51 may be employed as illustrated in FIG. 4.

As shown in FIGS. 3 and 4 the lossless transmission line 24 comprises a conductive tube 52 and a center rod 53. The tube 52 is mounted in openings 54 and 55 formed in flanges 56 and 57 of the rotor 13. The center rod 53 in turn is coaxially supported within the conductive tube 52 by means of insulating bushings 58 and feed through pins 61' of a typeshown to a larger scale in FIGS. 6. The feed through pins have heads 62 having a slightly convex surface to serve as fixed terminals for the electrical circuits through the feed through pins 61. Each of the feed through bushings 58 has a collar 63 which prevents it from sliding through the opening 54 in the rotor flange 56. The dimensions as such are to provide a press fit. The through-pin bushings 58, like other insulating elements in the apparatus are preferably comprised of an insulating substance having a very low loss at high frequencies, such as polytetrafluorethylene.

Each feed through pin 61 is formed with a conicalouter-surface, collar-like portion 64 which permits it to be driven into the opening in the bushing 58 but prevents withdrawal, to hold the pins 61 in place in the bushing 58. The feed through pin 61 has end portions 65 which in the case of the transmission line section 24 make electrical and mechanical connection with the center rod 53 by being pressed into suitable-dimension end opening 66 in the'rod 53.

However, in the case of the attenuation pads 15 to 23, the electrical and mechanical connection to the center conductor is accomplished by soldering or cementing the through pin portion 65 to the transition portion 39 of the center conductor means of the attenuator pad. As illustrated in FIG. 6 for example, a quantity of conductive epoxy cement 60 may be employed. Preferably, an epoxy cement with a high silver content is employed such as that produced by Epoxy Technology, Inc. of Watertown, Massachusetts having a volume resistivity of between 0.0001 and 0.0005 ohm'centimeter.

As illustrated in FIGS. 2 and 5, the fixed contact terminals 62 are arranged around the periphery of the rotor flanges 56 and 57 to enable the coaxial line connectors 32 and 33 to be connected to any selected one of the attenuator pads 15 to 23, inclusive, or to the lossfree coaxial line section 24. In addition, there are pins with heads 67 making contact directly with the rotor flanges 56 and 57, without insulation, for grounding the center conductors of the transmission line connectors 32 and 33 in one angular position of the rotor.

The coaxial line connectors 32 and 33 are in the form of specially constructed connector jacks having center conductor extensions 68 and 69 of resilient conductive metal such as beryllium copper serving as stationary contacts to cooperate with whichever one of the rotor switch contacts 62 or 67' is in the angular position to make electrical contact therewith. As illustrated in FIGS. 2 and 3, each coaxial connector jack assembly includes an outer conductor supporting flange 71, shown as square, with openings to 72 to receive machine screws 73 adapted to be threaded into threaded openings 74 in the housing 11, a center pin 75 spaced from the member 71 by a conventional insulating bushing 76, and a'grounding plate 77 having openings 78 aligned with the openings 72 and 74. The ground plates 77 may be secured between the connector jack flanges 71 and the flat surface of the housing 11 when the apparatus is assembled as illustrated in FIG. 1 and FIG. 3. The grounding plates 77 also have openings 79 to permit the center conductor pins 75 to extend into the housing 11 and are formed with bent down fins 81, so positioned as shown in FIG. 3 as to contact the end surfaces of the rotor flanges 56 and 57 electrically and mechanically to provide both axial alignment of the rotor 13 and to assure the grounding of the rotor 13 to the housing 11.

As shown in FIGS. 2 and 3, indexing mechanism is provided for retaining the rotor 13 in any one of a plurality of different angular positions for obtaining a selected degree of attenuations. On each such angular position one of the contact terminals 62 is in contact with the blades 68 and 69. The indexing mechanism includes the index plate 28, the ball detent 27, a ball retainer plate 82 and an index spring 83. As shown the ball retainer plate 82 and the index spring 83 are provided with screw receiving openings 84 to enable them to be secured to the end of the rotor 13 by means of conventional machine screws 85 received in threaded openings 86 in the rotor structure. As shown the diameter of a ball receiving opening 87 in the ball retainer plate 82 is very slightly larger than the diameter of the ball 27 so that the ball 27 is retained between the index spring 83 and the detent plate 28 and protrudes sufficiently to engage spherical surface depressions or dimples 88 in the index plate 28, so as to provide resilient means for holding the rotor 13 in one of its selected angular positions. As shown the index plate 28 is not rotatable but is held in fixed position by means of suitable screws 89 received in threaded openings 91 in the end face of the housing 11.

For the purpose of assuring that the outer silvered grounding edges 43 of the attenuator plates will be grounded to the housing 11, the attenuator pads are preferably wrapped along the outer edges by conductive braid 92 which is secured and electrically connected to the outer conductor tube 52 of the coaxial transmission line section 24, which is in turn supported and electrically connected to the flanges 56 and 57 of the rotor 13. As shown in the lower portion of FIG. 3 the braid 92 is of a woven construction adapted to expand from the slightly compressed position shown in FIG. 3 so as to assure electrical contact both with the outer edge 43 of each attenuator pad and the inner surface of the housing 11.

Since many changes could be made in the construction illustrated and many widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A variable attenuator comprising in combination a cylindrical, electrically conductive housing having lateral openings near the ends thereof,

connector means mounted on said housing at said openings, and

wherein the substrate is a ceramic plate with a deposited, thick-film resistive element supported on the first face of the substrate,'a pair of deposited conductive strips contacting the resistive element and a coating of deposited conductive material completely covering the reverse face of the substrate except for that portion directly opposite the resistive element, said first and second conductor material including fired silver layers on the edges of the substrate.

wherein said deposited conductive material is a coating of fired silver material.

a rotor rotatably mounted concentrically therewith in said housing comprising a central rotatable hub composed of electrically conductive material and a plurality of attenuator pads secured around said rotor, each pad comprising:

an insulating substrate secured to the hub and extending therefrom radially with an inner edge lying along the hub, an outer edge lying along the inner surface of the cylindrical housing, a first face and a reverse face lying in planes parallel to the rotor axis,

first conductor material on the substrate electrically contacting the rotatable hub,

second conductor material on the substrate with means for making electrical contact with the inner surface of the housing,

a resistive element on the first face of the substrate contacting said first and second conductor mate-. rial, and conductive means extending from said resistive element towards the ends of the substrate,

the rotor having a plurality of fixed terminals, each electrically connected to the end of one of said resistive elements, the housing having mounted thereon fixed blade means insulated from the hous- :5

ing, extending through the openings therein for contacting said rotor fixed terminals as the rotor is rotated to select a given pad. 2. A variable attenuator as described in claim 1 3. The variable attenuator described in claim 2 4. A variable attenuator as described in claim 2 5. A variable attenuator as described in claim 2 wherein transition elements are provided between each of the inner ends of the conductive strips and the center of each resistive element connected thereto.

6. A variable attenuator as described in claim 2 wherein transition elements are provided between the outer ends of said deposited conductive strips and the fixed rotor terminals.

7. A variable attentuator as described in claim 1 wherein coaxial connector means is mounted upon the conductive housing having'a center conductor and a fixed blade connected thereto contacting the fixed contacts of the rotor.

8. An attenuator pad comprising in combination: an insulating substrate having a first face and a reverse face, with a plurality of discrete resistive elements on the first face of the substrate; series conductive strips extending between said resistive elements and toward the ends of the substrate; and

conductor material on the reverse face of said substrate and electrically connected to portions of said resistive elements. 9. An attenuator pad as described in claim 8 having conductor material on the edges of the substrate electrically connected to the conductive material on the reverse face. 10. A miniature attenuator comprising a housing and a rotor having an electrically conductive hub carrying a resistive unit secured to the hub, said unit comprising:

an insulating substrate having a first face and a reverse face;

a resistive element supported on said substrate on said first face; a pair of conductive strips on said first face contacting the resistive element, and t a conductive layer on said substrate electrically connected to said resistive element and in electrical contact with said hub.

11. An attenuator as described in claim 10 having a plurality of said resistive units secured to the hub,

and

means for connecting said units sequentially as the rotor is rotated to select a given resistive unit.

12. An attenuator as described in claim 10 having a coating of conductive material covering the reverse face of the substrate except for that portion opposite the resistive element.

13. An attenuator comprising in combination:

an insulating substrate having a face and a reverse face;

coating material extending on the face in a band to form resistive attenuator element;

electrically conductive coating material in a microment.

$97553 UNITED STATES PATENT OFFICE ERTIFICATE OF CORRECTION Patent 1:0; 3,805,209 Dated April 16, 19 74 Robert M. Keranen It is certified that error appears in the above-identified patent. and that said Letters Patent are hereby corrected as shown below:

Col. 5, line 5, before "plane 42" insert ground- Col. 8, line 51, after "microstrip" insert -ground-.

Signed and sealed this 10th day of September 1971p;

(SEAL) Attest: I

MCCOY M. GIBSON, JR., e c. MARSHALL DANN Attesting Officer Commissioner of Patents wig? UNITED STA'IES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent No; 3 I 805 I209 D d April 16,- 1974 Robert M. Keranen It is certified that error appears in the above-identified patent and that sqid Letters Patent are hereby corrected as shown below:

Col. 5, line 5, before "plane 42" insert -ground- 7 Col. 8, line 51, after microstrip" insert -ground.

Signed and sealed this 10th day of Septer nb er' 197M.

(SEAL) Attes t:

McCOY 'M. GIBSON, JR, c. MARSHALL DANN Attesting' Officer Commissioner of Patents 

1. A variable attenuator comprising in combination a cylindrical, electrically conductive housing having lateral openings near the ends thereof, connector means mounted on said housing at said openings, and a rotor rotatably mounted concentrically therewith in said housing comprising a central rotatable hub composed of electrically conductive material and a plurality of attenuator pads secured around said rotor, each pad comprising: an insulating substrate secured to the hub and extending therefrom radially with an inner edge lying along the hub, an outer edge lying along the inner surface of the cylindrical housing, a first face and a reverse face lying in planes parallel to the rotor axis, first conductor material on the substrate electrically contacting the rotatable hub, second conductor material on the substrate with means for making electrical contact with the inner surface of the housing, a resistive element on the first face of the substrate contacting said first and second conductor material, and conductive means extending from said resistive element towards the ends of the substrate, the rotor having a plurality of fixed terminals, each electrically connected to the end of one of said resistive elements, the housing having mounted thereon fixed blade means insulated from the housing, extending through the openings therein for contacting said rotor fixed terminals as the rotor is rotated to select a given pad.
 2. A variable attenuator as described in claim 1 wherein the substrate is a ceramic plate with a deposited, thick-film resistive element supported on the first face of the substrate, a pair of deposited conductive strips contacting the resistive element and a coating of deposited conductive material completely covering the reverse face of the substRate except for that portion directly opposite the resistive element, said first and second conductor material including fired silver layers on the edges of the substrate.
 3. The variable attenuator described in claim 2 wherein said deposited conductive material is a coating of fired silver material.
 4. A variable attenuator as described in claim 2 wherein exposed flexible electrical conductor means is provided surrounding the pads providing ground connections between the outer edges of the pads and said outer housing.
 5. A variable attenuator as described in claim 2 wherein transition elements are provided between each of the inner ends of the conductive strips and the center of each resistive element connected thereto.
 6. A variable attenuator as described in claim 2 wherein transition elements are provided between the outer ends of said deposited conductive strips and the fixed rotor terminals.
 7. A variable attentuator as described in claim 1 wherein coaxial connector means is mounted upon the conductive housing having a center conductor and a fixed blade connected thereto contacting the fixed contacts of the rotor.
 8. An attenuator pad comprising in combination: an insulating substrate having a first face and a reverse face, with a plurality of discrete resistive elements on the first face of the substrate; series conductive strips extending between said resistive elements and toward the ends of the substrate; and conductor material on the reverse face of said substrate and electrically connected to portions of said resistive elements.
 9. An attenuator pad as described in claim 8 having conductor material on the edges of the substrate electrically connected to the conductive material on the reverse face.
 10. A miniature attenuator comprising a housing and a rotor having an electrically conductive hub carrying a resistive unit secured to the hub, said unit comprising: an insulating substrate having a first face and a reverse face; a resistive element supported on said substrate on said first face; a pair of conductive strips on said first face contacting the resistive element, and a conductive layer on said substrate electrically connected to said resistive element and in electrical contact with said hub.
 11. An attenuator as described in claim 10 having a plurality of said resistive units secured to the hub, and means for connecting said units sequentially as the rotor is rotated to select a given resistive unit.
 12. An attenuator as described in claim 10 having a coating of conductive material covering the reverse face of the substrate except for that portion opposite the resistive element.
 13. An attenuator comprising in combination: an insulating substrate having a face and a reverse face; coating material extending on the face in a band to form resistive attenuator element; electrically conductive coating material in a microstrip configuration extending on the face of said substrate from said resistive element; and a coating of electrically conductive material on the reverse face of said substrate forming a microstrip and end connections of the resistive element being connected to said microstrip ground for providing microstrip ground contact with said resistive element. 